In a radio receiver, a received radio signal is converted to provide an analog signal at a baseband frequency. Signal processing components, such as mixers, amplifiers and filters, each introduce their own DC content into the signal path of the analog system. Particularly where the analog signal contains signal content near the DC level and also particularly where conventional high gains are employed, such DC content distorts the signal. The DC content due to the signal processing components is referred to as offset.
Existing solutions for offset removal or reduction exist. Prior methods utilize AC coupling between amplifiers to remove DC content. However, this technique removes low frequency signal content of the data stream. Additionally, the reactances utilized in such systems lead to signal degeneration and slow response of the circuit to changing signal input conditions.
A particularly significant application of the present invention is in a solid state mobile telephone receiver using a single mixer, direct conversion architecture. A prevalent form of this receiver includes first and second baseband signal processing channels for respectively processing in-phase and quadrature components of any solid state receiver and signal processing chip or chips. The invention is applicable to other radio receivers than direct conversion receivers.